1. Field of the Invention
The present invention relates to injection molding machines, and, more particularly, to an injection unit with an adjustable granulate supply hopper which are detachably mountable in several different orientations on the die closing unit of an injection molding machine.
2. Description of the Prior Art
The injection of raw material into a closed injection molding die takes place either perpendicularly to the die separation plane, i.e. in a direction which coincides with the axis of die opening and closing movement, through an aperture in the stationary die carrier plate, or it takes place in the die separation plane, in a direction which is perpendicular to the movement axis of the die closing unit. Under certain circumstances, it may be desirable or necessary to inject simultaneously through the stationary die carrier plate and from one or more directions in the die separation plane.
An injection unit commonly has two parallel tie rods which carry the plastification cylinder and its drive on a longitudinally movable carrier bridge, the front extremities of the tie rods being attached to the die closing unit and the rear extremities being supported on the machine base, if necessary. It is known from the prior art to arrange such an injection molding machine in axial alignment with the die closing unit, for injection through the stationary die carrier plate, in which case the tie rods of the injection unit are preferably mounted in alignment with the two tie rods of the die closing unit, using suitable mounting sockets or the like. It is also known to arrange such an injection unit vertically above the die closing unit, in which case two tie rods of the injection unit are attached to the top of the stationary die carrier plate, or the two tie rods of the die closing unit, so that the injection unit is aimed for injection into the die separation plane from above. Both arrangements are well known and are disclosed in U.S. Pat. No. 3,086,244, for example. The same application also suggests the possibility of arranging the die closing unit itself in a vertical orientation, in which case an axially oriented injection unit would have to be arranged vertically above the die closing unit, while lateral injection in the die separation plane would require a horizontally arranged injection unit.
The selective horizontal or vertical orientation of the injection axis requires special adaptive capabilities of the supply hopper for the plastic granulate which is being fed into the plastification cylinder of the injection unit. Because the granulate is normally fed into the plastification cylinder under gravity, the granulate hopper must be made adjustable in its orientation relative to the injection unit axis. In U.S. Pat. No. 3,086,244, this adjustability is being achieved by using a supply hopper which is rotatably adjustable about the axis of an inclined connecting channel to the plastification cylinder, the hopper itself having a body which is angled-off from this adjustment axis. Such a rotatable hopper makes it possible to use the injection unit in either a horizontal or a vertical orientation, requiring merely a half-turn rotation of the hopper, for a substantially vertical orientation of the hopper in both cases.
One disadvantage of this type of hopper is that its body is one-sided, i.e. that its geometry deviates from that of a body of rotation and that it is therefore unsuitable for the use of a granulate stirring device inside the hopper.
Even with the aforementioned adjustability in the hopper connection, the injection unit is still limited to one of two mounting orientations: horizontal, with the tie rods side-by-side, or vertical. It follows that, when two or more injection units had to be arranged for injection into the die separation plane, this could only be done with a vertically oriented die closing unit.
From German Gebrauchsmuster (Utility Model) No. 66 03 267 it is known to connect a vertical hopper to a vertically oriented plastic extrusion cylinder by means of a short horizontal connecting cylinder which has a rotating feed screw arranged in its bore. This prior art device is specifically designed for the processing of liquified PVC into tubular parisons which are being fed into a bottle blowing die. The suggested application of this device does not involve the plastification of granular raw materials, but is in fact intended to avoid such plastification.